[wasm][eh] Add WebAssembly.Tag.toStringTag()

R=jkummerow@chromium.org

Bug: v8:11992
Change-Id: I4229a6fff8d956a5baa9ab9d5028f9abc20d4039
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3071405Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76109}

src/wasm/wasm-js.cc

@@ -2627,6 +2627,8 @@ void WasmJs::Install(Isolate* isolate, bool exposed_on_global_object) {
     JSFunction::EnsureHasInitialMap(tag_constructor);
     Handle<JSObject> tag_proto(
         JSObject::cast(tag_constructor->instance_prototype()), isolate);
+    JSObject::AddProperty(isolate, tag_proto, factory->to_string_tag_symbol(),
+                          v8_str(isolate, "WebAssembly.Tag"), ro_attributes);
     if (enabled_features.has_type_reflection()) {
       InstallFunc(isolate, tag_proto, "type", WebAssemblyTagType, 0);
     }

test/mjsunit/wasm/exceptions-api.js

@@ -30,6 +30,7 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
   assertThrows(
       () => builder.instantiate({ m: { ex: js_except_v }}), WebAssembly.LinkError,
       /imported tag does not match the expected type/);
+  assertTrue(js_except_i32.toString() == "[object WebAssembly.Tag]");
 })();
 
 (function TestExport() {